Duplicating carvers have been known for many years. Most have a router or other motorized cutting tool ganged to a stylus which is guided by the operator around a template. A master template is made up, which can be made of soft wood for ease of carving or from metal for longevity, and the template can be duplicated in hard wood or other material using the duplicating carver.
Two-dimensional carvers using pantographs (jointed parallelogram mechanisms) are familiar in the badge- and sign-making field. The stylus is traced around a path or groove in a template, and the router follows the same path to carve the letter or other design into wood or plastic blanks. The use of a pantograph allows increasing or decreasing the size of the sign relative to the template.
Three-dimensional duplicating carvers are similar, but add another degree of freedom to allow the duplicating carver to duplicate a three-dimensional original such as a propeller, sculpture, musical instrument, etc.
When one of the inventors herein was building an experimental aircraft, he found that the bored out, higher compression engine was significantly more powerful than a stock model "A" engine, putting out between 50 and 60 hp. This meant that he would have to experiment to get the optimum propeller.
When the time came to acquire a propeller, he was faced with the following options:
1. buy an inexpensive, lower quality, hand carved prop. PA1 2. buy an expensive, high quality propeller. PA1 3. inexpensively carve a high quality prop.
He decided to carve his own propeller. He was able to obtain the design for the original Pietenpol propeller (from the original propeller carver), along with recommendations on how to modify the design to pitch it correctly for the most efficiency. It would be very difficult to precisely carve two identical blades for a symmetrically accurate prop. A one-blade master propeller was carved, and it was decided to use a duplicator to carve two identical blades for the final propeller. This gave the option of modifying the master and easily carving additional props for changes in pitch, diameter, planform etc.
Getting an acceptable duplicator turned out to be the hard part. The inexpensive, plan-built, plywood carvers were not rigid enough for the accurate duplication needed. The mass produced general purpose duplicators were also too flimsy. An industrial duplicating mill was out of the question due to the extremely high cost. As a result, the present invention was designed to be the most accurate carver possible, but easy and simple to use, and less expensive than industrial mills.
Terrco, Inc., of Watertown, S. Dak., manufactures several general-purpose carving duplicators at this time.
The CM series uses a pantograph-like arrangement in which the stylus and router are each mounted on one end of two linked arms which are hinged at the other end to a pivot on a rod. The hinges allow the router/stylus to move roughly along a first horizontal axis (actually, along an arcuate path approximating the first axis). The pivot on the rod allows the router and stylus to move up and down in an arcuate fashion along the vertical axis. The rod is mounted at each end to slides, which allows the rod to slide along the third (second horizontal) axis. Thus, the cutter may move about all three axes. However, for very accurate carving, the semi-pantograph arrangement is too flexible, allowing the cutter to twist under the action of the router, and the arcuate movement of the arms in the horizontal plane makes it impossible to easily move the cutter straight along the axis.
The Terrco Duplicarver.TM. models mount the router and stylus to a horizontal rod. The router and stylus are fixed to the rod, but the rod is free to pivot in slides on each end, allowing the stylus and router to move in an arcuate fashion, primarily to allow the stylus and router to be swivelled fully horizontal, to work on vertical originals. The rod may also move in the slides from side to side along the first horizontal axis. The rod is mounted on the ends of a pivoting frame, which allows the rod (and hence the cutter and stylus) to move along the vertical axis (actually, along an arcuate path approximating the vertical axis). For motion on the second horizontal axis, the table upon which the workpiece and pattern are mounted must be moved fore-and-aft on a lower pivot arm. Once again, the arcuate movement for vertical motion is problematic, requiring simultaneous movement of the stylus and router on the guide rod, and the lower pivot arm and table, to travel a path along the vertical axis. The relatively thin guide rod introduces a degree of flexibility into the router which is also undesirable.
There have been many patents issued on carving duplicators. A few representative examples follow:
Babcock, PATTERN DUPLICATOR, U.S. Pat. No. 3,653,291 uses a vertically-suspended cutter and stylus. An overhead rail system is required, and the vertical motion is assisted with ropes, counterweights and pulleys. The wide frame is subject to torsional distortions, allowing the router and stylus to twist independently. No means is provided to limit the degrees of freedom of movement of the cutter. PA0 Hoenig, PANTOGRAPH APPARATUS, U.S. Pat. No. 3,739,824 is a duplicating carver intended for spindles. The router and stylus may slide on vertical shafts and the entire cutting mechanism slides on rails for movement along a horizontal axis. Mechanisms for rotating the spindle provide the motion of the workpiece about the second horizontal axis, rather than having the stylus/cutter assembly movable about three axes. PA0 Laskowski, THREE DIMENSIONAL DUPLICATOR ASSEMBLY, U.S. Pat. No. 4,078,474, and related U.S. Pat. No. 4,183,284, have the router and stylus are fixed to a shaft which is suspended by an "X" shaped frame. The other side of the frame is free to slide on a shaft which rolls on a wheel on each side along guide rails. The router and stylus are prone to unwanted motion due to the mounting on a relatively thin shaft which is free to rotate, and the "X" shaped support can twist about the thin center point, as well. The provision of single wheels on each end of the cross shaft allows the shaft to twist as it is rolled, introducing further distortions. PA0 Mitchell, THREE DIMENSIONAL DUPLICATING CARVING MACHINE, U.S. Pat. No. 4,278,117, also uses single wheels on each end of the cross shafts, with the same twisting problem as noted above. Again, the stylus and router are mounted on a relatively thin shaft, which can twist. PA0 Lenz, OUTBOARD TRACKING STATION FOR CARVING MACHINE, U.S. Pat. No. 4,288,185, moves the stylus outside the rails of the machine, to allow mounting a pair of routers inside the rails. The routers and stylus are mounted on relatively thin arms outward from a shaft, which allows for torsional distortion of both the arms and the shaft, and the shaft rolls on single wheels, allowing the same twisting problem as noted above. The arms swivel on hinges, as noted above for the Terrco Duplicarver.TM., with the same problem of arcuate side-to-side movement. PA0 Taylor, MACHINE TOOL, U.S. Pat. No. 5,256,011, also moves a cutting arrangement using a cross-shaft with single wheels, with the problems noted. The stylus and router pivot arcuately around two different axes, as well as sliding side-to-side along the shaft. The large torsion box is awkward and tends to block any view of the work to the rear.